UPMC Univ Paris 06, CNRS-FRE 3402, Biologie de l'ARN, 9 quai Saint Bernard, 75005 Paris, France.
Nucleic Acids Res. 2012 Oct;40(19):9557-70. doi: 10.1093/nar/gks762. Epub 2012 Aug 16.
The activating transcription factor 4 (ATF4) promotes transcriptional upregulation of specific target genes in response to cellular stress. ATF4 expression is regulated at the translational level by two short open reading frames (uORFs) in its 5'-untranslated region (5'-UTR). Here, we describe a mechanism regulating ATF4 expression in translation termination-deficient human cells. Using microarray analysis of total RNA and polysome-associated mRNAs, we show that depletion of the eucaryotic release factor 3a (eRF3a) induces upregulation of ATF4 and of ATF4 target genes. We show that eRF3a depletion modifies ATF4 translational control at regulatory uORFs increasing ATF4 ORF translation. Finally, we show that the increase of REDD1 expression, one of the upregulated targets of ATF4, is responsible for the mTOR pathway inhibition in eRF3a-depleted cells. Our results shed light on the molecular mechanisms connecting eRF3a depletion to mammalian target of rapamycin (mTOR) pathway inhibition and give an example of ATF4 activation that bypasses the signal transduction cascade leading to the phosphorylation of eIF2α. We propose that in mammals, in which the 5'-UTR regulatory elements of ATF4 mRNA are strictly conserved, variations in translation termination efficiency allow the modulation of the ATF4 response.
激活转录因子 4（ATF4）通过其 5'非翻译区（5'-UTR）中的两个短开放阅读框（uORFs）在翻译水平上调节其表达。在这里，我们描述了一种在翻译终止缺陷的人类细胞中调节 ATF4 表达的机制。通过对总 RNA 和多核糖体相关 mRNA 的微阵列分析，我们表明，真核释放因子 3a（eRF3a）的耗竭诱导 ATF4 和 ATF4 靶基因的上调。我们表明，eRF3a 的耗竭改变了 ATF4 翻译的调节 uORFs，增加了 ATF4 ORF 的翻译。最后，我们表明 REDD1 表达的增加，ATF4 的上调靶基因之一，是 eRF3a 耗竭细胞中 mTOR 途径抑制的原因。我们的研究结果阐明了连接 eRF3a 耗竭与哺乳动物雷帕霉素靶蛋白（mTOR）途径抑制的分子机制，并提供了一个绕过导致 eIF2α 磷酸化的信号转导级联激活 ATF4 的例子。我们提出，在哺乳动物中，ATF4 mRNA 的 5'-UTR 调节元件严格保守，翻译终止效率的变化允许 ATF4 反应的调节。
